Selective catalytic reduction (SCR):
SCR is considered as a mainstream technology of flue gas denitrification, denitrification efficiency is up to 90%.
Installing SCR devices generally in heat-engine plant have three forms:
1. High temperature and high dust type, SCR is located between the boiler flue gas outlet and air pre-heater;
2. High temperature and low dust type, SCR is located behind of high-temperature electrostatic precipitator (ESP);
3. Low temperature and low dust type, SCR is located behind of the flue gas denitrification device(FGD).
The advantage of the first arrangement is that the flue gas entering the reactor at temperatures above 300 degrees, most of the catalyst has sufficient activity at this temperature, the flue gas can be obtained good NOX purification effect without heating, but catalyst is at a high gas cloud of dust, the life will be affected adversely. K, Na, Ca etc. of fly ash will poison the catalyst to deactivate, fly ash wash and abrase reactor to cause. Catalyst clogging, if the flue gas temperature is too high will damage the catalyst sintering. However, if take appropriate method to prevent ash deposition, reduce washing, to prevent the temperature is too high or too low, can meet the design of a variety of conditions. Therefore, we use the first arrangement in the industry.
Refers to the role of a catalyst，take NH3 as a reducing agent, react with NOx selectively to generate N2 and H2O with non-toxic and non-pollution. SCR use reductant like ammonia or urea, at a certain temperature (optimum temperature 250°C---350°C), under the action of the catalyst by reduction NOx (NO,NO2) in the exhaust, converse NOx to non-pollution elements nitrogen molecules (N2).
Reaction as follows:
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